Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for multiple pieces of user equipment (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from the base station to the UE) and uplink channels (e.g., for transmissions from the UEs to the base station).
Some modes of communication may enable communications with a UE over different radio frequency spectrum bands (e.g., a licensed radio frequency spectrum band and/or an unlicensed or shared radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a licensed radio frequency spectrum band, offloading of at least some data traffic to shared radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. Prior to gaining access to, and communicating over, the unlicensed (or shared) radio frequency spectrum band, a transmitting apparatus may, in some examples, perform a listen before talk (LBT) procedure to contend for access to the unlicensed radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) to determine whether a channel of the shared radio frequency spectrum band is available. When it is determined that the channel of the shared radio frequency spectrum band is not available (e.g., because another wireless device is already using the channel of the shared radio frequency spectrum band), a CCA may be performed for the channel again at a later time.
In some cases, transmissions may be performed according to techniques to enhance the likelihood of channel access by wireless devices that seek to use shared radio frequency spectrum band. Some exemplary techniques may include allocating resources for channel for use by a UE in a synchronized manner. In some examples, multiple base stations and UEs may have synchronized CCA procedures and established protocols for when a base station or UE may perform a CCA during a coordinated CCA subframe, for example.